Sheet parameter measurement

ABSTRACT

A method and apparatus for assessing surface irregularities comprising directing a line beam at the surface, imaging the line on the surface formed by the line beam, and analysing data of the image to produce an objective indication of the degree of regularity of the surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is a divisional application of U.S.patent application Ser. No. 09/834,076, filed Apr. 12, 2001, which isherein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to the measurement of the mechanicalproperties of highly flexible or limp sheet material, for example paper,textile material, plastics and composite materials. In particular, theinvention relates to the measurement of the tensile, shear, buckling,and compression strengths, sheet thickness, bending stiffness andsurface qualities such as friction and roughness. The purpose of suchtesting—under normal loading without destruction of the sample of thematerial under test—is to determine the performance of the material inuse, e.g. clothing fabrics during normal wear.

[0003] To date, such measurements have generally been made independentlyon different samples of the material to be tested. For example, there isthe widely accepted Kawabata Evaluation System for Fabric (KESF) fortextile fabrics. With this system, different samples of the fabric to betested are required to be placed in several different devices in orderto make the measurements of the various properties listed above. Onesample of the fabric to be tested is placed in a device which measurestensile and shear properties by clamping the sample at two spacedlocations and moving the clamps apart and laterally relative to eachother. This device has to be calibrated for each measurement on asample. Bending strength, but not buckling, is measured by placing adifferent sample of the fabric in a second device. in this device thesample is mounted vertically and the device is very difficult to set upin trying to achieve an even tension in the fabric. One clamp makes acircumferential movement in order to measure the bending strength.Thickness measurement requires another measuring device. In this case ahead moves vertically relative to the fabric in order to measure thethickness of the material and then its compressibility. For surfaceproperties, a further sample of the material is clamped under load in afurther device in which a head lowers and the material is then movedlaterally relative to the head. Different probes on the head measuresurface roughness and friction. It is very expensive to have all ofthese devices and very time consuming to place the different samples inthe different devices in order to make all of the measurements. Anothersystem is the Fabric Assurance by Simple Testing (FAST) system.

[0004] This is a simplified version of the KESF system, but at least twodifferent samples are needed.

[0005] Thickness and compression are measured in one device at twopositions of a movable head.

[0006] Bending is measured in another device in which the fabric is laidon a bed and is traversed by a moving plate on top of the fabric untilthe fabric extends over the edge of the bed and cuts a light beam. Fortensile strength, the fabric is placed between two clamps in a furtherdevice, the lower one of the clamps being on an arm which is pivoted andhas a weight on the other end. When the arm is released, the deviceregisters the load in the fabric. The results from these tests arelimited to the measured loads only and cannot provide full stress/strainprofiles of the test samples. In addition the results from the two testsystems are not very reproducible, due to the need for different samplesizes and the manual handling for each test. In the cosmetics andmedical fields it is desirable to determine the effect cosmetic ormedical creams and the like have on the human skin. To this end a fabricwhich has similar characteristics to human or animal skin is treatedwith the cream and the mechanical properties of fabric are thenmeasured. For such an application the KESF and FAST systems areconsidered too expensive and too complicated.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a singleapparatus for the measurement of the mechanical properties of a singlesample of a limp sheet material in order to reduce the equipment costscompared with that of the number of existing devices required. It isalso an object of the present invention to reduce the time andcomplexity of making such measurements and to increase the accuracy andreproducibility of such measurements compared with the existing methods.

[0008] The invention provides a device for the measurement of themechanical properties of a limp sheet material, comprising a base, apair of clamping members operable to clamp the sheet material to thebase at spaced locations, load sensing means on at least one clampingmember, at least one of the clamping members being movable away from andtowards the other in the plane of the sheet material and laterally ofthe other in said plane, and a head assembly having a sensing devicespaced from the base and movable theretowards and laterally of the planeof the sheet material.

[0009] One clamping member may be the at least one movable clampingmember and the load sensing means may be mounted on the other clampingmember. Two load sensing means having differing ranges of measurementmay be mounted on the one clamping member, the first load sensing meansbeing adapted to measure tensile load and the second load sensing meansbeing adapted to measure buckling load. The measurement device maycomprise a third load sensing means adapted to measure shear loads. Thesensing device may comprise a further load sensing means and a surfacecharacteristics sensing means.

[0010] Preferably the base is a plate which is disposed substantiallyhorizontally, in which case the clamping members may be disposed abovethe base plate and positionally adjustable to clamp the sheet material.The measuring device may comprise position indicating means adapted toindicate the position of the at least one movable clamping memberrelative to a datum position. The at least one movable clamping membermay be mounted on low friction slideways, and the slideways may bedisposed remote from the axes of movement of the at least one movableclamping member. The head assembly may be disposed between the clampingmembers, and may be mounted on the base plate. The head assembly maycomprise a slide part on which the sensing device is mounted formovement towards the base plate and, together with the slide part,laterally of the sheet material.

[0011] The base plate may have an edge to a side of the at least onemovable clamping member remote from the other clamping member, overwhich edge the sheet material may he moved to cantilever thereover. Themeasurement device may comprise a beam transmitting device and a beamsensing device operable to receive the transmitted beam and detect whenthe sheet material interrupts the beam. The beam may be directed frombeneath and spaced from the edge of the base plate at an angle ofbetween 30° and 60° to the horizontal.

[0012] Preferably the beam is directed at an angle of 41.5° to thehorizontal. The base plate may be formed to have a shallow recessbetween the spaced locations to reduce the frictional contact betweenthe sheet material and the base plate.

[0013] The measurement device may comprise control means operable tocontrol the sequence of movement of the at least one movable clampingmember and the sensing device. The control means may also be operable torender operable the first or second load sensing means for measuringtensile load or buckling load respectively dependent on the direction ofmovement from the datum position of the at least one movable clampingmember. The control means may be operable to vary the length of timebetween successive movements of the at least one movable clamping memberand the sensing device. The control means may also be operable to adjustthe speed of movement of the at least one movable clamping member andthe sensing device. The control means may comprise programmable meansfor the selection of the measurements to be made, the speed of movementof the at least one movable clamping member and the sensing device, andthe timing of the movements.

[0014] The movement of the at least one movable clamping member and thesensing device may be effected by respective stepper motors. Theclamping members may also be moved between respective sample materialrelease positions and their clamping positions by respective steppermotors.

[0015] In another aspect, the invention relates to methods and apparatusfor the assessment of seam pucker and other surface irregularities.

[0016] Assessment of surface irregularities, particularly seam pucker,is at present largely a subjective matter. Attempts to introduceobjectivity into the assessment have, to date, not been so successful asthe result is non-standard. The same is true for measurements,generally, of surface irregularities of which seam pucker istypical—with the exception, possibly, of microscopic surface roughnessmeasurements, necessarily automated and standardized because ofinaccessibility to the naked eye—surface irregularity is “judged” ratherthan objectively measured.

[0017] The invention provides an objective assessment for seam puckerand other, comparable surface irregularities.

[0018] The invention comprises a method for the assessment of seampucker and other surface irregularities comprising directing at thesurface a line beam from an illuminator, imaging the line on the surfaceformed by the line beam and analysing data of the image to produce anobjective indication of the degree of irregularity of the surface.

[0019] Parallel line beams may be directed at the surface. For theassessment of seam pucker, the parallel line beams may be directed toform lines on the surface parallel to and either side of the seam, andat an angle from the plane perpendicular to the surface.

[0020] The illuminator may comprise a line beam laser.

[0021] The line on the surface may be imaged by a pixel image such as aCCD array camera.

[0022] The image may be analysed in a computer programmed with imageanalysis software. The result of analysing the image may be a display ofa distribution of severity of deviation of the surface from flat.

[0023] The surface may be that of a limp material, such as a textilefabric, mounted on a flat support base. The base may, for theassessment, be inclined steeply with the material clamped uppermost andresting against the base below the clamping location.

[0024] For consistency of measurement the material is preferably thesame size as the bed, so no additional irregularity is occasioned byedge effects. A sample for assessment may be cut to size using the bedas a template.

[0025] The invention also comprises surface irregularity assessmentapparatus comprising

[0026] a line beam illuminator;

[0027] a support arrangement for the surface under assessment such thatthe line beam illuminator is directed at the surface to illuminate aline thereon;

[0028] an imaging arrangement adapted to image the line illuminated onthe surface, by the line beam illuminator; and

[0029] analysis means adapted to receive image data to produce anobjective indication of the degree of irregularity of the surface.

[0030] There may be one, two or more line beam illuminators castingparallel beams. Beams may be cast in different arrangements to providefurther information.

[0031] The imaging arrangement may comprise a pixel imaging arrangement,and may comprise a CCD array.

[0032] The line illuminator may be a laser.

[0033] The analysis means may comprise a computer programmed with imageanalysis software.

BRIEF DESCRIPTION OF THE FIGURES

[0034] Embodiments of the invention will now be further described withreferences to the accompanying drawings in which:

[0035]FIG. 1 is a front elevation;

[0036]FIG. 2 is a view on line 2-2 of FIG. 1;

[0037]FIG. 3 is a perspective view of an apparatus for measuring seampucker, in simplified form;

[0038]FIG. 4 is a view of an illuminated sample in the apparatus of FIG.3; and,

[0039]FIG. 5 is a block diagram of the apparatus of FIG. 3.

DETAILED DESCRIPTION

[0040] Referring now to FIGS. 1 and 2, there is shown a measurementdevice 10 comprising a substantially horizontally disposed base plate 11on which a sample 12 of the material to be tested is placed. A ‘fixed’clamping member 13 and a ‘movable’ clamping member 14 are mounted onrespective supports 15, 16 and are movable by respective stepper motors17, 18 from their respective sample material release positions as showndownwardly towards the base plate 11 to clamp the sample 12. At thisinitial stage the ‘movable’ clamping member 14 and its ‘movable’ support16 are in the ‘datum position and the end of the sample 12 is alignedwith the end 19 of the base plate 11. Mounted on a head support 20 is ahead assembly comprising a slide part 20 a which is movable by means ofstepper motor 21 and lead screw laterally of the sample 12 in slideways22 and a sensing part 20 b which is movable by means of a stepper motor23 vertically in slideways 24. The sensing part 20 b has a sensingdevice 25 which incorporates load sensing means 26 and a surfacecharacteristics sensing means 27. A position sensor 28 is provided onthe support 20 to measure the height of the head assembly 20 relative tothe base plate 11.

[0041] The ‘movable’ support 16 is mounted on the base plate 11 in lowfriction slideways 29 disposed remote from the axis 30 of movement ofthe ‘movable’ support 16 to minimise the effects of friction on theoperation and measurement sensitivity of the measurement device 10. The‘movable’ support 16 is movable by means of stepper motor 31 and leadscrew 32 away from and towards the ‘fixed’ support 15, and a positionsensor 33 indicates the position of the ‘movable’ support 16 relative toa datum position. The upper part 16 a of the ‘movable’ support 16 ismovable in slideways 34 in lower part 16 b by stepper motor 35 laterallyof the base plate 11. A position sensor 36 indicates the lateralposition of the ‘movable’ support 16 relative to a datum centralposition. In fact, the ‘fixed’ support 15 is also mounted on theslideways 29 and is movable from its datum position 16 under the effectof a change in the tension in the sample 12. Any such change in tensionis detected by load cells 37, 38. The ‘movable’ support 16 may beextended as shown to support the sample 12 when it is moved towards theedge 19 of the base plate 12 for the bending test described below.

[0042] Located adjacent the edge 19 of the base plate 12 is a beamtransmitting device 39 and a beam sensing device 40 operable to receivethe transmitted beam 41 and detect when the sample 12 interrupts thebeam 41. The beam transmitting device 39 is mounted at the edge 19 andthe beam 41 is directed downwardly towards the base plate 11 at an angleof 41.5° to the horizontal.

[0043] A control device 42, including programmable means 43, is providedto control automatically the operation of the measuring device 10, whichis as follows. The prepared sample 12 of the material to be tested isplaced in the measuring device 10 on the base plate 11 so that the endof the sample aligns with the edge 19 of the base plate 11. The controldevice 42 is activated and the clamping members 13, 14 are lowered bytheir motors 17, 18 to clamp the sample 12. Load cell 37, having a rangeof measurement appropriate to the measurement of tension in the sample12 is brought into operation by the control means 42 and the other loadcell 38 is taken out of operation. The motor 31 is then operated to movethe ‘movable’ support 16 from its datum position in a direction awayfrom the ‘fixed’ support 15. This movement applies a tensile load to thesample 12, which is measured by the load cell 37. A shallow recess 44 inthe base plate 11 under the sample 12 reduces the effect of frictionbetween the sample 12 and the base plate 11. The distance moved by the‘movable’ support 16 is measured by the position sensor 33, so that a‘load-extension’ relationship for the sample 12 can be determined. Thecontrol means 42 reverses the motor 31 to return the ‘movable’ support16 to its datum position. The load sensor 37 is taken out of operationand the load cell 38, having a range of measurement appropriate to themeasurement of buckling load in the sample 12, is brought intooperation. Further movement of the ‘movable’ support 16 towards the‘fixed’ support 15 enables the load in the sample 12 as it buckles to bemeasured by the load cell 38. The ‘movable support 16 is then againreturned to its datum position.

[0044] The sensing part 20 b of the head support 20 is then lowered bymeans of the motor 23 until contact between the sample 12 and thesurface characteristics sensing means 27. The height of the surfacecharacteristics sensing means 27 above the base plate 11 is indicated bythe position sensor 28 so as to determine the thickness of the sample12. Further lowering of the sensing part 20 b will apply a compressiveload to the sample 12, as determined by the load cell 26. Correlation ofthe readings of the load cell 26 and the position sensor 28 will providea ‘Load-compression’ relationship for the sample 12. The sensing part 20b is then raised to the position of contact between the sample 12 andthe surface characteristics sensing means 27. Lateral movement of theslide part 20 a along slideways 22 by means of motor 21 causes thesurface characteristics sensing means 27 to measure the friction betweenit and the sample 12 and also the surface roughness of the sample 12.The sensing part 20 b is then raised to its original position.

[0045] The control means 42 then activates motor 36 to move the upperpart 16 a of the ‘movable’ support 16 laterally of the base plate 11.This induces a shear in the sample 12, and the shear load is indicatedby a further load cell 45. Correlation of the readings of the load cell45 and the position sensor 36 will provide a ‘Load-shear’ relationshipfor the sample 12.

[0046] To determine the bending characteristics of the sample 12, thecontrol means 42 now activates motors 17 and 18 to raise the ‘fixed’ and‘movable’ clamping members 13, 14 to release the sample 12. Motor 31 isthen activated to move the ‘movable’ support 16 and the sample 12 awayfrom the ‘fixed’ support 15. During this movement the sample 12 issupported by the extended support 16 c. This causes the end of thesample 12 to cantilever over the edge 19 of the base plate 11 eventuallyto bend and hang downwardly 50 as to interrupt the beam 41. The positionsensor 33 indicates the amount of sample 12 extending over the edge 19of the base plate 11 when the beam 41 is interrupted, this amount beingdependent on the stiffness of the material of the sample 12.

[0047] If not all of the above measurements are required, suitableprogramming of the programmable means 43 can cause the control means 42only to activate the relevant motors for the measuring device to performthe required operations. Furthermore, if the effect of the speed ofapplication of any load to the sample 12 is required, the programmablemeans 43 can be programmed to alter the speed of operation of therelevant motor or motors. As a further benefit of the measuring device10, cyclic loading of the sample 12 may be effected by suitableprogramming of the programmable means 43.

[0048] Alternative embodiments of the measuring device according to theinvention will be apparent to persons skilled in the art. For example,as an alternative to stepper motors, the movements of the movable partsof the measurement device may be effected by pneumatic or hydrauliccylinders or by linear motors. As another alternative construction, theslide and sensing parts 20 a, 20 b may be mounted on the upper part 16 aof the ‘movable’ support 16. By means of the present inventionmeasurements of tensile, shear, buckling, and compression strengths,sheet thickness, bending stiffness and surface qualities such asfriction and roughness can be made on a single sample of a limp sheetmaterial in a single measuring device, thereby reducing the timeinvolved in performing the tests and the initial cost of purchasing thenecessary equipment.

[0049] FIGS. 3 to 5 of the drawings illustrate a fabric sample 311 witha seam 312 giving rise to seam pucker undulations 13 in the fabriceither side of the seam 312—held by a clamp 314 on a support base 315inclined steeply so the fabric rests on the base rather than hangsfreely, but otherwise without any constriction that would give rise tospecious undulation or flattening and of any pucker that might bepresent. A bridge 315 a on the support base 315 restricts movement ofthe sample 311 during monitoring.

[0050] The base 315 is removable from an enclosure in which theassessment is carried out and may be used as a template in cutting asample for assessment from a larger piece.

[0051] Two parallel line beam lasers 316, 317 are directed at the sample311 so that they illuminate lines 318 either side of the seam 312.

[0052] As seen in FIG. 4, these lines take on a undulating appearancebecause of the seam pucker. The sample is imaged by a CCD camera 319,which is arranged at such a distance from the sample that thedistortions due to seam pucker in the lines 318 are visible in theimage.

[0053] The whole is enclosed, for the assessment, in a box, and should,to prevent laser light escaping that might damage eyes be vieweddirectly, there being an interlock arrangement to ensure the laserscannot operate unless the box is closed.

[0054] The image from the camera 319 is fed to a computer 321, FIG. 5,with a vision card 322 and software capable of analysing the image bysuitable routines to assess the degree and spatial frequency of anyundulation caused by seam pucker.

[0055] Clearly a similar set-up can be employed to assess other types ofsurface irregularity.

[0056] The apparatus may readily be miniaturized and presented as ahand-held arrangement for portable use.

I claim:
 1. A method for the assessment of seam pucker and other surfaceirregularities comprising directing at the surface a line beam from anilluminator, imaging the line on the surface formed by the line beam andanalysing data of the image to produce an objective indication of thedegree of regularity of the surface.
 2. The method of claim 1, in whichparallel line beams are directed at the surface.
 3. The method of claim2, in which the parallel line beams are directed to form lines on thesurface parallel to and either side of the seam, and at an angle from aplane perpendicular to the surface.
 4. The method of claim 1, in whichthe illuminator comprises a line beam laser.
 5. The method of claim 1,in which the line on the surface is imaged by a pixel imager, such as aCCD array camera.
 6. The method of claim 1, in which the image isanalysed in a computer programmed with image analysis software.
 7. Themethod of claim 6, in which the result of analysing the image is adisplay of a distribution of severity of deviation of the surface fromflat.
 8. The method of claim 1, in which the surface comprises a limpmaterial, such as a textile fabric mounted on a flat support bed.
 9. Themethod of claim 8, in which the flat support bed is, for the assessment,inclined steeply with the material clamped uppermost and resting againstthe bed below the clamping location.
 10. The method of claim 8, in whichthe material is the same size as the bed.
 11. A method of claim 10, inwhich the material is cut to size using the bed as a template. 12.Surface irregularity assessment apparatus comprising: a line beamilluminator; a support arrangement for the surface under assessment suchthat the line beam illuminator is directed at the surface to illuminatea line thereon; an imaging arrangement adapted to image the lineilluminator on the surface by the line beam illuminator; and, analysismeans adapted to receive image data to produce an objective indicationof the degree of irregularity of the surface.
 13. The apparatus of claim12, in which there are one, two or more line beam illuminators castingparallel beams.
 14. The apparatus of claim 12, in which the imagingarrangement comprises a pixel imaging arrangement.
 15. The apparatus ofclaim 14, in which the pixel imaging arrangement comprise a CCD array.16. The apparatus of claim 12, in which the line illuminator and theimaging arrangement point at the surface from different directions. 17.The apparatus of claim 12, in which the line illuminator is a laser. 18.The apparatus of claim 12, in which the analysis means comprising acomputer programmed with image analysis software.